Interlocking engagement for a plastic blank



c. E. PALMER 3,019,957

INTERLOCKING ENGAGEMENT FOR A PLASTIC BLANK Feb. 6, 1962 Filed April 7. 1959 /8 20 A? l620 M INVENTOR. 3 CHAPLE5 E. PALMER ATTORNEYS 3,019,957 INTERLDCKING ENGAGEMENT FOR-A \PLASTICBLANK Charles Pahner, Turnpike Road, $omers, Conn. Filed Apr. 7, 1959, Ser. No. 804,686 3 Claims. (Ci. 229-46 This invention relates to containers formed from blanks, and more particularly to a novel interlocking engagement for panels of'a plastic container blank.

Inrecent'years, great'emphasis has been placed upon transparent packaging in an attempt'to increase consumer appeal. Various forms of'containers have been utilized, but semi-rigid structures have generally been molded with resultant high cost. More'recently, the folding of plastic semi-rigid sheet stock has become feasible, However, because of the nature of plastics, the interlocks formed by incising the sheet have generally crazed, split. or torn as a result of stresses placed upon them.

The present invention is directed to a novel interlock for plastic sheet material which distributes the stress placed thereon, and substantially eliminates tearing, crazing, or splitting of the sheet. Other advantages will be apparent from the following detailed description and the attached drawing wherein:

FIG. 1 is a perspective view of a container embodying the invention;

FIG. 2 is a blank for forming the container of FIG. 1;

FIG. 3 is a front elevational view of the container in FIG. 1 with the interlocks in partial engagement; and

FIG. 4 is an exploded section along the line 44 of FIG. 1. 7

Referring in detail to the drawings, a plastic package utilizing the novel interlocking engagement of the present invention is therein illustrated and designated generally as 2. The container 2 has been folded from the blank illustrated in FIG. 2 to provide a base panel 4, side panels 6, end panel 8, top panel 10 and locking panels 12. As illustrated, reinforcing flaps 14 are desirably provided on the end panel 8, and the corners of the end panel 8 are preferably provided with a circular or arcuate incision 9 to distribute stresses and substantially eliminate crazing and tearing.

The panels are engaged by the interlock of the present invention'which is best shown in FIG. 2, wherein on one of the panels to be engaged, a substantially U-shaped incision 16 is provided and on the other, a curvilinear incision 18 is made consisting of a centrally disposed arcuate tab portion 20 and a pair of reverse curves 22 smoothly blending into the center arcuate portion. The tab 20 and the U-shaped incision 16 both point in the direction of separation of the panels.

The incisions are so dimensioned that the ends of the I base of the U-shaped incision 16 intersect the curvilinear incision 18 at about the centers of the reverse curves 22, as illustrated in FIG. 1. The incisions 16 and 18 are spaced inwardly from the free ends of their respective panels so that upon assembly the side panel 6 will abut against the top panel 10.

In operative engagement of the interlock, the center portion 20 and a portion of the reverse curves 22 extend through and outwardly of the slit formed by the base of the U-shaped incision. The stress of the interlock is thus directed against the corners (which are preferably rounded) and base of the U-shaped incision 16, and the central portion of the reverse curves 22.

However, because of the configuration of the interlock incisions, the stress is not concentrated at any single point, but is translated over a large distance of the curvilinear incision, and of the U-shaped incision, thus minimizing stress at the ends of the incisions.

3,919,957 'Fatente'd Feb; 6, 1562 ice 2 Alternatively, aslot withrounded corners may replace the U 'shaped incision illustrated, although the disposal of'the 'excised'plastic makes such a practice less desirable, "In'this embodiment, the'e'nds-of the-slot should also intersect the slit at about the center of the reverse curve portion-and the outer peripheryof the base. As is readily apparent, the outer periphery 'of thebase and sideso'fthe siotwillstill define a substantially U-shap'e'd incision.

The positive clampingaction of the overlockof the presenti'nvention is best understood by reference to FIG. 4. Th'econfiguration'ofthe curvilinear incision 18enables the arcuate tab 20 to "be flexed inwardly out of the plane of-the lockingpane'l 12 without tearing theplastic sheet, the revers'ely curved end portions 22 distributing the stress and contributing to the resiliency'in-the tab 20. The-tabZl) inthe lockingpanel 12 passes through the 'slit provided b'ythe base'of the U-shaped incision 16 in the side panel'fi and then along theinner surfaceof the side'panel 6,'the resiliencyof the plastic sheet maintaining close engagement between the tab and panel. Similarly, the tab provided by the U-shaped incision 16 is-distorted-out'of its plane by the insertion of tab 20 and is pressed against the tab 20 by'the inherent resilience of the plastic sheet so that a complete clamptype overlock is provided, as clearly shown in FIG. 4. This clamp-type'overlock prevents the panels from separating when subjected to forces in the planes of the overlying panels while also holding the overlying panels in close lateral contact by reason of the clamp design and the inherent resilience of the plastic sheet.

The interlock of the present invention has been found greatly superior to conventional slit and tab designs, and has been free from tearing and splitting even after considerable use and stresses. It has enabled the use of an economical mechanical engagement for panels even where considerable wear is to be encountered, and has been particularly advantageous in folded packages made from oriented polystyrene sheet.

Although but one embodiment of the invention has been illustrated, it is understood that modifications may be made without departing from the spirit of the invention.

Having thus described the invention, I claim:

1. A container formed from plastic sheet and having a first panel extending in one direction in overlying relationship to a second panel, said first panel having a curvilinear incision therein spaced inwardly from the free end thereof, saidcurvilinear incision having a substantially arcuate center portion and a pair of reverse curves smoothly blending into said center portion, said arcuate center portion defining an arcuate tab having its free end extending away from the free end of said first panel, said second panel having a substantially U-shaped slit therein with a base portion and legs extending oppositely of said arcuate tab, said arcuate tab extending through the base portion of said U-shaped slit and inwardly of the container with the reverse curve portions of said incision bottoming against the base portion of said slit, said tab extending along the inner wall of said second panel and resiliently bearing upon the surface thereof to maintain said panels in assembly against movement opposite to said one direction to prevent separation thereof, and means on said container to limit movement of the first panel in said one direction so as to prevent disengagement thereby.

2. A container formed from plastic sheet and having an outwardly disposed locking panel extending in one direction along the outer surface of a wall panel, said locking panel having a curvilinear incision therein spaced inwardly from the free end thereof, said curvilinear incision having a substantially arcuate center portion and a pair of reverse curves smoothly blending into said center portion, said arcuate center portion defining an arcuate tab having its free end extending away from the free end of said locking panel, said wall panel having a substantially U-shaped slit therein with a base portion and legs extending oppositely of said arcuate tab and defining a second tab extending in the direction of said arcuate tab, said arcuate tab extending through the base portion of said U-shaped slit and inwardly of the con tainer with the reverse curve portions of said incision bottoming against the base portion of said slit, said legs of the U-shaped incision intersecting said curvilinear incision at about the center of said reverse curves, said arcuate tab extending along the inner wall of said Wall panel and resiliently bearing upon the surface thereof and said second tab resiliently bearing upon said tab to maintain said panels in clamping assembly against movement opposite to said one direction to prevent separation thereof, and means on said container to limit movement of the locking panel in said one direction so as to prevent disengagement thereby.

3. A blank of plastic material having contiguous panel portions for folding into a transparent container when erected, at least one of said panel portions being adapted to extend in one direction along the outer surface of a second panel, said one panel having a curvilinear incision therein spaced inwardly from the free end thereof, said curvilinear incision having a substantially arcuate center portion and a pair of reverse curves smoothly blending into said center portion, said arcuate center portion defining a substantially arcuate tab having its free end pointing away from the free end of said one panel, said second panel having a substantially U-shaped incision therein with a base portion and legs extending away from the free end thereof, said incisions being dimensioned and located on said panels for passage of said arcuate tab through the base portion of said U-shaped incision upon erection of the container with the reverse curve portions bottoming against the base portion of the U-shaped incision with the legs intersecting the centers of said reverse curves, said arcuate tab being adapted to extend along the inner. surface of said second panel and resiliently bear thereon, and said container having means thereon to limit movement of said one panel in said one direction.

References Cited in the file of this patent UNITED STATES PATENTS 210,576 Taylor Dec. 3, 1878 1,950,934 Shearer Mar. 13, 1934 2,764,461 Montgomery Sept. 25, 1956 2,918,205 Zeitter Dec. 22, 1959 2,956,720 Rindal Oct. 18, 1960 FOREIGN PATENTS 493,410 Great Britain Oct. 7, 1938 

